Radio apparatus



A. M. WENGEL RADIO APPARATUS Nov.. 26, `1935.

M M Y FiledA July 3l, 1953 Patented Nov.4 26, 1935 UNITED STATES rArEN'T orricr:

2 Claims.

The invention relates to radio apparatus and is particularly adapted to be embodied in radio receivers but the invention is limited to this use only to the extent indicated in the appended 5 claims.

A particular object of the invention is to provide an improved radio receiver which will operate efliciently and economically with a power supply of uni-directional current such as a plurality of dry cells or storage batteries providing A, B and C voltages. Y

Another particular object of the invention is to provide an improved heterodyningv stage in radio apparatus of the heterodyning type.

Another p-articular object of the invention is to provide improved radio apparatus wherein a single vacuum tube which utilizes the filament as a cathode will function efficiently and economically as a detector and an oscillator.

Still another object of the invention is to provide radio receivers operated by power supplies of dry cells or storage batteries and having a high degree of sensitivity comparable with that of radio receivers having more stages of ampliication and having power supplies operated by alternating current supplied by central stations. Y

Other objects and advantages will become apparent as the following detailed description progresses, reference being had to the accompanying drawing, the figure in the drawing being a circuit diagram of a superheterodyne radio receiver which embodies the invention.

Referring to the drawing, wherein a preferred embodiment of the invention is illustrated, the reference character IB designates the antenna circuit of a radio receiver of the heterodyne type which also comprises a stage II of tuned radio frequency, a combined first detector and oscil- 40 lator stage I2, a stage I4 for amplifying the intermediate frequency, a second detector stage I5 and an audio power amplifying stage I6.

The antenna circuit I0 is of a conventional type and preferably comprises a potentiometer 25 and the primary winding of a transformer 2l, the primary winding of the transformer 2| being provided preferably with a single turn 22 which is wound around the outer side of the secondary winding of the transformer 2l.

The radio frequency amplifying stage ll preferably comprises a tuned grid circuit 23, a screen grid tube 24 and a resistor 25, the resistor being connected in series between the secondary winding of the transformer 2I and a grid bias potentiometer 21 which forms part of a power Aor storage batteries.

(Cl. Z50-20) supply designated generally by the reference character 33. It will be noted that the grid bias potentiometer 21 is also connected to a ren sistor 3| interposed between the potentiometer 2 and a tuned grid circuit 32 forming part of 5 the intermediate frequency amplifying stage i4.

The potentiometers 2l] and 2l are operated preferably by a single control and form a volume control.

The radio frequency amplifying stage II is 10 connected operatively to lthe combined first detector and oscillator stage I2 by a transformer 33, the secondary winding of which is part of a tuned grid circuit 34 forming part of the stage I2. The stage I2 comprises a screen grid tube 15 of the tuned grid circuit 32. The stage I4 pref- 25" erably comprises a screen grid tube 4I which may be of the same type as the screen grid tube 35 although in someinstances it may be preferable to employ tubes of other types such as a pentode tube. 30

The stage I4 is connected operatively to the second detector stage I5 by a transformer 43, the secondary winding of which forms part of a tuned grid circuit 44. The control grid associated with the tuned circuit 44 is part of a 3547" screen grid Atube 45 which, in this instance, is of identical construction with. the tube 35 described above. The grid of the tube 45 is connected to the tuned circuit 44 through a conventional grid leak and a condenser which are 40 shown at 46.

The second detector stage I5 is connected operatively to the audio power amplifying stage I6 by resistance coupling means 48, the plate circuit of the tube 45 being provided with a filter 45 53 to prevent the transfer of radio frequencies from the stage I5 to the stage I6.

The stage I6 is of a conventional type and preferably comprises a pentode tube 5I. In this instance the stage I5 comprises asound repro- 50 ducing device IUE.

The power supply 30 preferably comprises a B battery 55 formed of a plurality of dry cells The negative terminal of the B battery 55 is connected to the negative 55 end of an A battery 56 through resistors 51 and 58 and the resistor of the potentiometer 21. The battery 55 preferably comprises a plurality of dry cells or a storage battery. A condenser 5@ interposed between the negative terminals of the batteries 55 and 56 and connected in parallel with the resistors 51 and 53 and the resistor of the potentiometer 21 functions as a bypass for audio frequencies. The negative terminal of the B battery 55 is connected to the control grid of the tube 5| through a resistor 65.3 which forms part of the resistance coupling t8, the other resistor of this resistance coupling being identified by the reference character 5l. Obviously, the connection between the negative terminal of the battery 55 and the control grid of the tube 5I provides the grid bias for the tube 5|.

The negative terminal of the A battery 55 is connected to a negative filament bus 65 which is common to the tubes described above. The positive terminal of the battery 56 is connected to a positive filament bus 65 which is common to the tubes described above.

The positive terminal of the battery 55 is connected to a bus 38 which is connected operatively to the plates of the tubes described above. The screen grids of the tubes 24, 35 and 4| are connected operatively to a bus SS connected to the batt ry 55 to provide the desired voltage. The screen grids of the tubes 45 and 5I are connected operatively to the bus 53. The space charge grid of the tube 5I is connected to the filament of the tube.

For convenience, the elements of the tube 35 are designated as follows: The filament is 36, the control grid is 35a, the screen grid is 35h and the plate is 35e. The negative end of the lament 3G is connected to one end of a. radio frequency choke coil lll which has its other end connected to the negative filament bus 55 and also to one terminal of a condenser 'H adapted to by-pass radio frequencies from the screen grid 35 back to the filament 36. The other terminal of the condenser 'H is connected to the screen grid 35h. The screen grid 35h is also connected to one end of a resistor 13 which has its other end connected to the screen grid bus 69. The positive end of the filament 36 is connected to one terminal of a condenser 'l5 and to one terminal of a primary winding 16 forming part of a transformer 'l'i having a secondary winding '58. The other terminals of the condenser 'l5 and the primary winding 16 are connected to the positive filament bus 56 and to the tuned circuit 34.

The plate 35e is connected to one end of the primary winding of the transformer 40, which primary winding has its other end connected to one end of the secondary winding or coil T8 and to one terminal of a Xed condenser winch its other terminal connected to one terminal of a variable condenser 35, the remaining terminal of the condenser 86 being grounded. The remaining terminal of the secondary winding 18 is connected to one end of a resistor 8l and to one terminal of a condenser 88 which has its other terminal grounded. The remaining terminal of the resistor Bl' is connected to the bus 58. The primary winding -of the transformer 4! is preferably shunted by a xed condenser 9E), the condenser 5@ and the primary winding associated with it having constants ofv such value that they form a circuit tuned to the intermediate frequency. It may be mentioned at this point in the description that the circuit 32 is also preferably tuned to the intermediate frequency.

The resistor 8l is provided to prevent the transfer of radio frequencies from the oscillator to the power supply 3d. The secondary Winding 78 and the condensers 35 and 36, and to a slight extent the condenser 88, constitute a tuned circuit IIE! for the oscillator. The circuit H0 being tuned preferably to the oscillator frequency. The rotors of the variable condensers provided in the 1:) tuned circuits 23 and 34 and the rotor of the variable condenser 8B are mounted preferably on a single shaft to be controlled by a single dial. The radio receiver is tuned to various frequencies by displacing the rotor of the condenser 1; 83 and the rotors of the condensers in the tuned circuits 23 and 3d.

It will be readily understood that the tuned circuit which comprises the condenser s@ and the primary winding of the transformer lili offers 20 large impedance to the intermediate frequency but relatively little impedance to the oscillator requency. Therefore, there will be a relatively large transfer of energy at the intermediate frequency from the primary winding of the transformer 40 to its secondary winding as there will be a relatively large drop in the intermediate frequency potential across the primary winding.

It is also readily understood that the tuned circuit. I l0 in the plate circuit of the tube 35 offers 20 large impedance to the oscillator frequency, but relatively little impedance tothe intermediate frequency. This construction insures that there will be a large transfer of energy at the oscillator frequency from the winding 18 to the primary 35 win-ding 'i6 which may be designated as a pick-up coil. The radio frequency choke 10 insures that the potential developed at oscillator frequency across the terminals of the winding 16 will not be shorted through the power supply. The condenser 15 and the winding'l are. preferably tuned 4U to the oscillator frequency and this tuned circuit is designated by the reference character 80.

The tuned circuit I ID co-operates with the tube 35 and the primary winding 16 to generate the local oscillations. radio frequency is impressed upon the grid 35a, the signal will heterodyne With the oscillator frequency and provides the intermediate frequency which is transferred from the primary winding of the transformer 40 to the secondary Winding 50' thereof.

It will be readily apparent to those skilled in the art that the stage l2 may be employed in a superheterodyne circuit in such manner that the oscillator tube 35 will amplify the intermediate 55 frequency.

In some embodiments of the invention, I contemplate employing a variable condenser 15. When the condenser 'l5 is a variable condenser, the rotor thereof will be operated preferably by 30 the same control which displaces the rotors of the condenser 8'! and the rotors of the condensers in the tuned circuits 23 and 34. However, as indicated abo-ve, the preferred embodiment of the inventio-n comprises a fixed condesser 15 which tunes 65 the circuit 8!! to the order of the oscillator frev quency, the rotors of the condenser 86 an-d the rotors of the condensers in the tuned circuits 23 and 35i being actuated by a single control.

A feature -of the invention is the sensitivity of 70 the improved circuit, which sensitivity permits the use of dry cells as A, B and C power supplies.

While I have shown and described certain em- When an incoming signal at 45t' bodiments of my invention, it is to be understood that it is capable of many modifications. Changes,

therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims, in which it is my intention to claim all novelty inherent in my invention as broadly as possible, in View of the prior art.

I claim:

l. In a radio receiver of the heterodyne type, adapted to be battery operated; a vacuum tube including a grid, a plate, and a directly heated lament serving as a cathode; grid, plate, and filament circuits connected toV said grid, plate, and filament, respectively; a tuned circuit and a radio frequency choke coil in series with said directly heated lament, said tuned circuit being in the grid circuit of said tube; two tuned circuits in series in the plate circuit, said circuits being tuned to different frequencies, and one of said circuits being tuned to substantially the same frequency as the first mentioned tuned circuit and inductively coupled thereto, whereby said tube generates local oscillations of a frequency tively; a tuned circuitV in said grid circuit, said 10 tuned circuit comprising an inductance and a fixed condenser; a second tuned circuit in said plate circuit, said second tuned circuit comprising an indutance and a variable condenser, said second tuned circuit being tuned to lsubstantially 15 the same frequency as said first tuned circuit; a third tuned circuit in said plate circuit in series with said second circuit and tuned to a different frequency and means whereby said two first-mentioned tuned circuits are inductively 20 coupled, whereby said tube generates local oscillations of a frequency substantially equal to the frequency of said coupled tuned circuits.

ARTHUR M. WENGEL. 

